1. Field of the Invention
This invention relates to methods and apparatus for protecting living systems from adverse effects upon them of electric fields, magnetic fields and electromagnetic fields.
2. Background and Discussion of Related Art
For some years past there has been a growing recognition and concern that humans are suffering adverse effects, notably cancers, from living and/or working in ambient electromagnetic fields, particularly those fields which are alternating or pulsating or being modulated at frequencies below 500 Hz. Ambient frequencies particularly identified with an enhanced risk of cancer are those "power" frequencies at 60 Hz (U.S.) and 50 Hz (U.K. and continental countries). Electromagnetic fields existing near devices using cathode ray tubes also are implicated, due to fields generated by the magnetic electron beam deflecting devices included in the tube control apparatus.
Various articles have been published on the electromagnetic field problem. Over the past 11 years a series of epidemiological studies have found that low level electromagnetic fields [even as low as 1 .mu.T (1 micro Tesla) for 60 Hz power line fields] can be correlated with increased incidence of certain diseases. This correlation is strongest for those who have lived or worked in this environment for many years. For example, an increased risk of cancer has been found among children who lived for several years close to power lines (Wertheimer, N. and Leeper, E. "Electrical Wiring Configurations and Childhood Cancer", AM. J. EPIDEMIOLOGY, 109. 273-284 (1979); also, Savitz, D. A. et al., "Case Control Study of Childhood Cancer and Exposure to 60-Hertz Magnetic Fields," AM. J. EPIDEMIOLOGY, 128, 10-20 (1988); also, Milham, S. Jr., "Increased Mortality in Amateur Radio Operators Due to Lymphatic and Hematopoietic Malignancies," AM. J. EPIDEMIOLOGY, 128, 1175-1176 (1988). The research indicates that children from high electromagnetic field exposure homes have a 50 percent greater risk of developing cancer, particularly leukemia, lymphomas, and nervous system tumors. Other data also show that men working in electrical jobs, such as electricians and telephone lineman are at higher risk for brain tumors and other cancers. In a recent study in the Los Angeles area, S. Preston-Martin and collaborators at the University of Southern California found that men who had worked for 10 years or more in a variety of electrical occupations had a ten times greater chance of getting brain tumors than men in the control group. [Preston-Martin, S., and Mack, W. and Peters, Jr. "Astrocytoma Risk Related to Job Exposure to Electric and Magnetic Fields," presented at DOE contractors Annual Review, Denver Colo., Nov. 5-8, 1990.] A study performed by G. Matanoski of Johns Hopkins University found a dose response relationship for cancers in male New York Telephone employees from 1976 to 1980. [Matanoski, G., Elliot, E. and Breysse, P. Poster presented at the annual DOE/EPRI Contractors Review of Biological Effects from Electric and Magnetic Fields, November 1989, Portland, Oreg.] Matanoski measured the average magnetic field exposure among different types of employees and then installation and repair workers. A comparison of the cancer rates among the various types of employees showed that cable splicers were nearly twice as likely to develop cancer as those employees who did not work on telephone lines. Among central office workers those who were exposed to the short intense fields of telephone switching equipment the rates of occurrence of cancers were unusually high, although not as high as for cable splicers. The central office workers were more than three times as likely to get prostate cancer and more than twice as likely to get oral cancer as co-workers who were less exposed. And there were two cases of male breast cancer, a disease so rare that no cases at all would be expected.
The 60 Hz electromagnetic fields found in residential settings can vary from about 0.05 .mu.T to over 1000 .mu.T. In-vitro experiments have definitely shown that changes in biological cell function can occur in fields as low or lower than 1 .mu.T and as high as 500 .mu.T. R. Goodman and collaborators [Goodman, R. and Henderson, A., "Sine Waves Enhance Cellular Transcription,"BIOELECTROMAGNETICS, 7, 23-29, 1986)] have shown that RNA levels can be increased by electromagnetic fields ranging in frequency from 15 to 4400 Hz with amplitudes of 18 to 1150 .mu.T. They have shown that the RNA levels can be enhanced by factors of ten or more. Jutilainen and coworkers [Jutilainen, J., Laara, E. and Saali, K., INT. J. RADIAT. BIOL.,52, 787-793, (1987)] have shown that 1 .mu.T 50-Hertz electromagnetic fields can induce abnormalities in chick embryos. Thus, electromagnetic fields appear not only to be carcinogenic, but also capable of inducing birth defects. Pollack and collaborators, C. T. Brighton, E. O'Keefe, S. R. Pollack and C. C. Clark, J. ORTH. RES. (to be published), have shown that electric fields as low as 0.1 mv/cm at 60 kHz can stimulate growth of bone osteoblasts. McLeod and collaborators have found that in the region between 1 Hz and 100 Hz, much lower fields are needed to stimulate fibroblast growth than at frequencies above and below this range [McLeod, K. J., Lee, R. and Ehrlich, H., "Frequency Dependence of Electric Field Modulation of Fibroblast Protein Synthesis," SCIENCE, 250, 1465 (1987)].
Reported related research on animals is not as extensive as for humans, but there is every reason to believe that the same adverse effects occur in them as in humans. Therefore, protection of living systems including but not limited to humans and animals are encompassed within the present invention.